The overall goal of this program is to develop strategies for the correction of inherited diseases of bone marrow-derived cells by genetic modification of hematopoietic stem cells. The specific aims of this proposal are focused on the use of recombinant retroviral and adeno- associated virus (AAV) vectors for gene transfer into primitive hematopoietic stem cells. The specific diseases targeted are two forms of severe combined immunodeficiency (X-linked and adenosine deaminase deficiency), S-linked chronic granulomatous disease (CGD), and Fanconi anemia Group C. Protocols will be developed for the efficient transduction of human hematopoietic stem cells with retroviral and AAV vectors. The relative merit of different sources of human hematopoietic stem cells as targets for these viral vectors will be evaluated. The feasibility of incorporating ex vivo expansion to increase the number of stem cell targets will also be investigated. Finally, recombinant viral vectors will be identified that result in high level, stable, and functional expression of the transduced gene in progeny of hematopoietic stem cells. Experimental approaches will include the use of in vitro culture systems, xenographic animal models, and a murine model of X- linked CGD. The implementation of these aims will be shared among 4 projects and 3 core units. This proposal draws from a group of investigators with diverse but complementary experience in hematopoiesis and stem cell biology, retroviral- and AAV-mediated gene transfer, molecular genetics, virology, bone marrow transplantation, and neonatology. Achievement of these goals will permit the translation of this basic work to the development of clinical protocols for effective viral-mediated gene transfer therapy of genetic blood diseases. On a broader level, these studies should provide insight into the biologic behavior of hematopoietic stem cells and the ability to manipulate them ex vivo.